Heavy duty machining and working operations to which the invention pertains are characterized by use of relatively high forces to shape workpieces both by cutting and non-cutting processes. Such operations include non-cutting shaping processes such as forging, stamping, spinning, extruding, rolling, drawing and ironing and cutting processes such as punching, shearing, and broaching, as well as high force drilling, grinding, milling and turning processes. Characteristic of heavy duty machining operations, work done on the workpiece together with friction between the tool and workpiece generate sufficient heat to distort the workpiece and cause high rates of tool wear. Hence, it is well known in the art of such heavy duty machining operations to apply a machining fluid (e.g. metalworking fluid) composition to the interface between the tool and the workpiece to reduce friction and remove heat.
Machining fluids are generally broadly classified into two categories: non-aqueous (i.e. oils); and, aqueous (i.e. water based). As oil based fluids are known to pose difficulties relating to disposal, in-use mist generation, and flammability, there is an increasing demand for aqueous based fluids for use in heavy duty machining operations.
Aqueous based machining fluids are complex combinations of water, lubricants and additives such as for example extreme pressure agents, surfactants, corrosion inhibitors, fungicides, bactericides, antifoam agents and settling agents. Aqueous based machining fluids are known in the art to be classified into soluble oils, synthetic and semi-synthetic types. Of these types, only synthetic fluids are characterized as true solutions, soluble oils employing special mineral oil that disperses in water to form an opaque emulsion, and semi-synthetics comprising emulsions of oil and water made transparent or translucent by use of high concentrations of emulsifiers (see Tooling and Production March 1986, p. 38). It is well known that fluids containing components tending to emulsify petroleum oils are prone to emulsify tramp oils (i.e. oils leaking from and around machine tools) that contribute to generation of mists in use and to increased susceptibility to the growth of bacteria and fungi in the fluid.
As synthetic type aqueous machining fluids generally do not contain such petroleum oil emulsifying components, such fluids are less likely to emulsify tramp oils. Additionally synthetic type aqueous machining fluids have often been found to permit easier cleanup in and around machining operations as well as easier cleanup of the machined parts. These advantages have led to an increased utilization of synthetic type aqueous machining fluids (e.g. metalworking fluids) in metalworking processes. While synthetic type aqueous metalworking fluids have been successfully used in light duty metalworking processes (i.e. processes employing relatively low mechanical forces), known synthetic type aqueous fluids lack lubricity comparable to fluids known for heavy duty machining processes. In particular, fluids known for heavy duty machining processes commonly include chlorine and/or sulfur containing lubricants which are only slightly soluble in water and, hence, are absent in synthetic fluids. Thus there has been and continues to be the need for improving the performance of synthetic type aqueous machining fluids especially in relation to their use in heavy duty metalworking processes.
The art has used various approaches to improve aqueous machining fluids for use in heavy duty metalworking processes. A combination of a water soluble polyoxypropylene/polyoxyethylene glycol block copolymer and a water emulsifiable high pressure chlorinated paraffin, sulfurized ester of fatty acid or chlorinated ester of fatty acid lubricant in an aqueous metalworking fluid has been proposed in U.S. Pat. No. 4,212,750. In U.S. Pat. No. 3,995,465 a water based cold forming lubricant containing a block copolymer having a polyoxypropylene center moiety with oxyethylene grafted on to its ends which precipitates out of solution at elevated temperatures in combination with an alkali saponified sulfurized or chlorinated triglyceride is described. An aqueous solution or emulsion functional fluid (e.g. cutting fluid) employing an alkenyl substituted carboxylic agent/hydroxy terminated polyoxyalkylene reaction product thickening agent is proposed in U.S. Pat. No. 4,659,492. A water based metalworking lubricant containing a water soluble oxyalkylene derivative of an amine (e.g. polyalkylene polyamine, alkyl amine, alkaryl amine and carboxylic acid amine) and a phosphorus bearing acid or derivative thereof (e.g. butyl acid phosphate, phosphoric acid and butyl phosphonic acid) or boric acid is described in U.S. Pat. No. 4,626,367. A completely hydrophilic phosphated polyethoxylated n-butane-1,4-diol in a synthetic aqueous metalworking fluid has been proposed in U.S. Pat. No. 4,177,154.
It is also known in the art of emulsion type aqueous metalworking fluids, e.g. U.S. Pat. No. 5,706,684, to employ sulfurized and/or chlorinated lubricants (e.g. sulfurized olefin) as extreme pressure lubricants in combination with fatty acids (e.g. tall oil fatty acid) or fatty acid salts (e.g. alkanolamine salt of stearic acid) and ethylene oxide/propylene oxide copolymers having at least one terminal hydroxyl group and organic phosphates (e.g. poly-(1,2-ethanediyl) alpha-isodecyl-omega hydroxy phosphate) for heavy duty machining of metals. Such known aqueous metalworking fluids are known to exhibit such draw backs as emulsifying tramp oil contaminants, staining metal parts and leaving residues which are difficult to wash off, potentially interfering with subsequent coating, plating, and joining processes.
It is therefore an object of this invention to provide a synthetic aqueous machining fluid for improving mechanical working and shaping processes on metallic and non-metallic workpieces. Another object of this invention is to provide a synthetic aqueous machining fluid for improving heavy duty mechanical working and shaping processes on metallic workpieces. A further object of this invention is to provide a synthetic aqueous machining fluid having improved lubricity especially usable in heavy duty mechanical working and shaping processes on metallic workpieces. A still further object of this invention is to provide a synthetic aqueous machining fluid overcoming disadvantages of prior art aqueous and non-aqueous oil based machining fluids. A still further object of this invention is to provide improved methods of machining employing synthetic aqueous machining fluids in accordance with the invention.